As a typical example of a display device, a liquid crystal display device and an organic EL (electroluminescence) display device respectively having a liquid crystal element and a light-emitting element in each pixel are represented. These display devices have a display element such as a liquid crystal element and an organic light-emitting element (hereinafter, referred to as a light-emitting element) in each of a plurality of pixels formed over a substrate. A liquid crystal element and a light-emitting element include a liquid crystal and a layer containing an organic compound (hereinafter, referred to as an organic layer), respectively, between a pair of electrodes and are driven by applying a voltage or supplying a current to the pair of electrodes.
Since a light-emitting element is an all-solid display element, display quality is not influenced in principle even if a display device is provided with flexibility and folded or bent. This feature has been utilized to fabricate a so-called flexible display (sheet display) in which a light-emitting element is formed over a flexible substrate. For example, a flexible organic EL display device which is foldable is disclosed in Japanese patent application publication 2013-15835.